The invention relates to pressure balancing valves as used for plumbing fittings, such as shower and tub control valves.
When operating bathtub spouts and shower heads, an undesirable situation usually arises when the pressure of either the hot or cold water line is sharply reduced or increased, as may occur from simultaneous operation of some other device joined in the same plumbing network, or from some malfunction in the water source itself. Upon such an occurrence, the user of the spout or shower head may be scalded by a sudden drop in the cold water pressure, or conversely distressingly chilled by a cutback in the hot water pressure. By employing a pressure balancing valve in the supply lines, such situations are substantially eliminated by automatically equalizing the water pressures at the outlets of the valve. By regulating the pressures, a preselected temperature of the mixed hot and cold water is maintained at the tub spout or shower head. Also, in the event of complete loss of one or the other water sources, the flow of water will be sufficiently throttled in time to prevent large quantities of untempered water from causing undue discomfort.
One type of pressure equalizing or proportioning valve is the sliding piston type, as disclosed in U.S. Pat. No. 2,200,578 issued to T. C. Mahon on May 14, 1940. Such a valve consists of a body having fluid flow passageways and a piston floating between and intersecting the passageways. An increase in inlet pressure in one passageway will cause an axial sliding displacement of the piston towards the opposite passageway. This increases the rate of fluid flow in one passageway and simultaneously decreases the fluid flow in the opposite passageway, until a condition of equilibrium is attained at which point the outlet pressures in the two passageways are substantially equal. While sliding piston arrangements perform in a generally satisfactory manner, mineral and sediment depositions occur frequently and tend to "freeze" the axial shifting of the piston causing a loss of fluid pressure regulation at the outlets of the valve. When used in a tub-shower application, such imbalance results in discomforting temperature variation and water pressure cutback.
Attempts to alleviate these aforementioned fluctuations have produced a diaphragm actuated type of balancing valve, such as that disclosed in U.S. Pat. No. 3,688,790 issued to H. Esten on Sept. 5, 1972. Constructions of this type feature a body having spaced flow paths interconnected by an intermediate chamber across which a resilient diaphragm extends. Secured transversely to this diaphragm member is a piston rod, or valve stem assembly, having radially enlarged head elements which serve to open and close ports in the flow paths. An imbalance of inlet water pressure on one side of the diaphragm will cause it to deflect in the opposite direction and displace the piston rod and valve heads until a state of pressure equalization at the outlets of the valve is reached. Utilization of the diaphragm-sliding piston valve arrangement eliminates somewhat the liming and particle deposition problems formerly encountered in prior valves; however, fluid turbulence in this type of valve can appear and cause overcompensation, diaphragm oscillation, or water hammer, all of which impair a proper balance of the fluid flow rates and severely hamper the stability of the device.
It is desirable to furnish a pressure balancing valve which is self-purging, such that sedimentation problems are substantially alleviated. In addition, a pressure balancing valve should be sensitive, such that it will respond to small pressure variations at the inlets to the valve and effectively check water hammer. In the event of a complete loss of pressure in one of the supply lines, it is desirable characteristic that there be a substantial shutoff in the other line to prevent high flow discharges of only hot or cold water.
From a commercial standpoint, a pressure balancing valve should also be simple and compact in construction, and perform reliably and accurately while requiring a minimun of close manufacturing tolerances.
It is against this background of the art that the present invention has been conceived, and a principal goal of the invention is to provide an improved pressure balancing valve which has greater stability and sensitivity, and fewer operating malfunctions than prior pressure balancing devices.